1. Field of the Invention
The present invention relates generally to image processing apparatus and, more particularly, to an image processing apparatus for storing image data in a page memory while rotating the image data sequentially fed by 0.degree., 90.degree., 180.degree. or 270.degree. in real time.
2. Prior Art
Heretofore, there has been proposed an apparatus for storing image data in a page memory while rotating the image data sequentially fed by 90.degree. (Japanese Patent Laid-Open No. 235181/1990). In such an apparatus, it has been arranged that one page of a rotated image is ultimately obtained through the steps of reading one word from an address in a page memory including a bit position where image data that have been fed is disposed, designating the bit position in the word, rewriting the data at that bit position by means of the image data thus fed, and writing the rewritten data to the address of the page memory again.
Further, in image processing apparatus, the number of density gradations per pixel is determined by the number of information bits. If the number of information bits is 1, a two-gradation monochromatic image will be reproduced and if it is 2, a variable density four-gradation monochromatic image will be reproduced. Although the number of information bits per pixel is normally fixed, the practice commonly followed is to change the number of information bits for the purpose of image processing in the same image processing apparatus. For instance, when monochromatic binary image data is processed, the number of information bits is set at 1 and when image data having a half tone is processed, the number of information bits is increased. When an image is rotated in such an image processing apparatus, an image rotational process is needed for image data different in the number of information bits per pixel.
Japanese Patent Laid-Open No. 81657/1985, for instance, discloses a system of controlling addresses in a memory by exerting increment/decrement control over a counter as a data control system of an image rotating apparatus. In the control system described in that Gazette, no inconvenience arises as long as the number of information bits representing a pixel is fixed. When the number of information bits per pixel is varied, however, a plurality of address control means are required for each data bit and this tends to make the apparatus complicated. As a result, the process of rotating an image has been impossible to attain only by exerting increment/decrement control over the counter when input images are different in the number of information bits per pixel. Moreover, the image data fed from a scanner and the like has been impossible to rotate in real time before being stored in a page memory.
Moreover, Japanese Patent Laid-Open No. 83153/1960 discloses a data storage unit for rotating an image having a block of N-bit.times.N-bit at high speed by a cyclic shift. However, it has also been infeasible to rotate image data of one page at high speed by rotating a plurality of blocks collectively because the image data has to be input to this storage unit block to block.
Notwithstanding, the process steps of reading one word from an address in the page memory, rewriting a part of the word by means of the image data that has been fed, and writing the rewritten part to the same address in the page memory again have to be completed each time image data is fed after the image rotating method in the prior art apparatus. For this reason, high-speed processing has been impossible in the aforementioned apparatus since the speed at which the image data is fed cannot be higher than the speed at which the page memory is accessed.